Ranking of factors determining potassium mass balance in bicarbonate haemodialysis

Abstract

Our studies enabled to establish the ranking of factors determining intradialysis K(+)MB: plasma K(+) → dialysate K(+) gradient is the main determinant; acid-base balance plays a much less important role. The duration of HD session per se is an independent determinant of K(+)MB.

Dialysate bicarbonate concentration: Too much of a good thing?

“…A randomized controlled trial showed an association between higher D BIC and a faster decrease in intradialysis plasma K + concentration . The true challenge in patients undergoing HD is to avoid both life‐threatening predialysis hyperkalemia (plasma K + level >6 mmol/L) and postdialysis relative hypokalemia (or at least very rapid decrease in plasma K + level, and the related risk of lethal arrhythmias); Arrhythmias and prolongation of the QT interval . The QT interval is a recognized electrocardiographic marker of the ventricular repolarization and its prolongation has been associated with increased risk of sudden death in both pathological and healthy populations .…”

“…32 A randomized controlled trial showed an association between higher D BIC and a faster decrease in intradialysis plasma K + concentration. 33 The true challenge in patients undergoing HD is to avoid both life-threatening predialysis hyperkalemia (plasma K + level >6 mmol/L) and postdialysis relative hypokalemia (or at least very rapid decrease in plasma K + level, and the related risk of lethal arrhythmias) 34 ;…”

Dialysate potassium concentration: Should mass balance trump electrophysiology?

“…After the initial acute fall in serum potassium levels in the first hour, a more gradual decline of an additional 1 mEq/L occurs over next 2 hours as the serum‐to‐dialysate potassium gradient narrows. During the final hour, serum potassium levels remain steady even though diffusive clearance is still occurring, indicating equilibrium between the rates of potassium removal and the rate of re‐equilibration from intracellular space . At the conclusion of treatment, there is a subacute “rebound” of serum potassium levels with continued movement of potassium from intracellular space to extracellular space.…”

“…Second, although the effect of dialysate magnesium concentration on potassium kinetics has not been studied, low dialysate magnesium could potentiate risks associated with low potassium dialysate in a similar fashion via promotion of intracellular potassium shifts, given the effects of hypomagnesemia on risk of hypokalemia . Third, convective clearance of potassium plays a small but significant role in total dialytic potassium removal; recent mass balance studies have shown that potassium mass removed by ultrafiltration accounts for approximately 6% of the total potassium mass removed . Finally, glucose‐free or low glucose containing dialysate solutions can also lead to higher potassium removal via suppression of insulin‐mediated shifts of potassium to the intracellular space …”

“…The effects of extending dialysis treatment time on potassium kinetics was examined in a crossover study comparing patients assigned to either a 4‐hour or an 8‐hour dialysis which were pair‐matched for dialysate potassium concentration, total dialysate volume, and total ultrafiltration volume . With the extended treatment times, there was a slower rate of serum potassium fall, a 15% overall increase in total potassium removal, and an identical end‐of‐treatment serum potassium in 8 hour treatments compared to 4 hour treatments.…”